We have focused our attention on the interaction of Campylobacter jejuni with human epithelial cells particularly with respect to altered protein synthesis that occurs during the binding and internalization of C. jejuni. Antisera prepared against organisms grown in the presence of epithelial cells are capable of inhibiting translocation and have been used to screen recombinant expression libraries of C. jejuni genomic DNA. Several clones have been identified that produce proteins that are preferentially recognized by antisera produced against bacteria cultured with epithelial cells. One clone was completely sequenced and appears to encode the homolog of the low molecular weight, bacterial DNA-binding protein HU. The promoter structure and other regulatory elements of the gene have been mapped. In addition, we have identified and characterized an intron-like element in the 235 ribosomal subunit genes of C. jejuni. Additional studies have characterized in vitro phenotypic passage variants of C. jejuni. A high passage variant of a clinical isolate termed M96 that is defective for internalization within epithelial cells has also been obtained. However, this variant is fully competent at translocating across monolayers of polarized epithelial cells. At the molecular level the strain differs only from the parent in terms of the structure of lipopolysaccharide (LPS). The specific differences in structure are being characterized.